1. Field of Invention
This invention relates generally to syringes, and more particularly, to syringe assemblies wherein unintentional exposure is preempted utilizing permanent needle retraction and cylinder sealing.
2. Description of Prior Art
The simple sealed cylinder, permanently-affixed needle and movable plunger arrangement of a conventional syringe provides a number of desirable qualities. In addition to reliability and low cost, the tube is gripped, the needle maneuvered and the plunger depressed utilizing a single, well established and non-distracting one-handed motion. Such operation is critical in the often frantic health care environment. However, used syringes pose a serious health risk due to: (1) scraping or pricking of the skin by an exposed needle; (2) accidental secondary injection (3) ingestion or often even mere contact with residual chemicals and/or bodily fluids escaping from a discarded syringe. Disposal of syringes therefore extends the risk beyond the health care environment.
Simple screening type solutions, while retaining the simple syringe mechanism, are plagued with inherent problems. Needle caps are subject to loss, improper affixing and dislodging. Syringe disposal containers add inordinate expense. In addition, both introduce additional attention-diverting, unfamiliar, two-handed manipulation into a time/procedure critical environment.
Attention has therefore shifted to modifying the syringe mechanism itself; more specifically, to safety syringes wherein, following syringe use, an augmented plunger dislodges the needle which is then drawn into the cylinder. Hailer, U.S. Pat. No. 4,026,287 (snap-fit and screwable plunger-to-needle head interfaces), McGary, U.S. Pat. No. 5,053,010, Bin, U.S. Pat. No. 4,955,869 and Terrill, U.S. Pat. No. 4,978,340 (pressure fit plunger to needle head or head assembly interfaces), Haber, U.S. Pat. No. 4,908,022 (suction cup interface), Chen, U.S. Pat. No. 5,242,402 (needle angularly engaged), DeChellis, U.S. Pat. No. 4,921,486 (dislodge interface and needle spring mechanism), Wallingford, U.S. Pat. No. 5,098,390 (reusable needle).
One disadvantage of these assemblies is that the needle remains subject to further depression of the plunger, thereby again potentially exposing the needle. Proposed solutions either fail to solve this problem or create further problems. The angular needle retraction proposed by Chen remains subject to foreseeable pressure on the plunger, as does the "floating" catapulted needle of DeChellis. A perforated, breakaway plunger "handle" proposed by Haber et al, U.S. Pat. No. 4,826,484, presents reliability questions during use and requires unconventional manipulation and disposal. Utilizing the threaded plunger-to-cylinder-cavity locking mechanism disclosed by Harris, U.S. Pat. No. 5,222,944, similarly requires added manipulation that is distracting to immediate life-saving concerns.
A second disadvantage is the complexity of the proposed mechanisms, which necessarily increases cost, compromises reliability and may well impede acceptance by practitioners.
A third disadvantage is that these assemblies fail to address the problem of sealing the cavity that remains after the needle is retracted. The singular, molded plug mechanism posed by Chen is complex, subject to failure and adds considerable expense to syringe manufacture. In addition, offset needle positioning for special applications denies sufficient space for such a method.
Thus there is a need for a safety syringe that reliably and inexpensively retracts the needle, assures that the needle will remain retracted and seals the needle cavity following syringe use; a safety syringe that further accomplishes these goals through user manipulation commensurate with that required for a conventional syringe.